<meta charset="UTF-8">
<style>
    body{
        background-image: url(./花.jpeg);
        background-size: 100% 100%;
    }
</style>
<div style="font-size: 50px;position: absolute;">🐝</div>
<script>
    document.onmousemove = function(evt){
        var e = evt || window.event
        var divObj = document.querySelector('div')
        divObj.style.left = e.clientX - divObj.offsetWidth/2 + 'px'
        divObj.style.top = e.clientY - divObj.offsetHeight/2 + 'px'
    }
</script>